Hydrodynamic brake

ABSTRACT

A hydrodynamic brake for a vehicle having a stator and a rotor, which each comprise an annular recess and a plurality of vanes which are provided in the respective recess. The rotor rotates in a rotation direction such that a relatively high pressure is created on a first side of the respective vanes of the stator and a relatively low pressure on a second side of each vane of the stator. This pressure difference is used for the supply and the discharge, respectively, of the fluid. A respective supply opening is provided in the stator in the vicinity of the second side of a respective vane and a respective discharge opening is provided in the stator in the vicinity of the first side of a respective vane.

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a hydrodynamic brake and particularlyto a brake which moves fluid rapidly into and out of the brake.

Auxiliary brakes are principally used in heavy vehicles, such as lorriesand buses, in order to avoid wear of the ordinary brakes of the vehicle,such as the service brakes, for example at braking on long downhillslopes. An example of such an auxiliary brake is a hydrodynamicretarder, which generates a braking moment by means of any suitable oilbetween a stator and a rotor. The stator and the rotor constitutetogether a toroid-shaped space, which is called torus. The stator aswell as the rotor is provided with a plurality of vanes and the oil isguided during the rotation of the rotor by the vanes within thetoroid-shaped space. During the braking process, the kinetic energy ofthe oil is transformed to heat energy. The oil has to be cooled after ithas left the toroid-shaped space. Thereafter the oil may again besupplied to the toroid-shaped space. The retarder is connected to thepower train of the vehicle, for example, at the propeller shaft inconnection to the gearbox of the vehicle for allowing braking of thedriving wheels of the vehicle. The retarder may be provided directly onthe propeller shaft or be connected to that shaft via a gear unit. At alow number of revolutions of the propeller shaft and when the spacebetween the stator and the rotor, i.e. the toroid-shaped space, isfilled with oil, the braking effect of the retarder increases with therate of rotation of the propeller shaft, and the output braking momentof the retarder is substantially proportional to the number ofrevolutions of the propeller shaft. Consequently, at a certain number ofrevolutions of the propeller shaft, a certain maximum output brakingmoment may be obtained. At higher number of revolutions of the propellershaft, the output braking moment depends on the coefficient of fullnessof oil in the toroid-shaped space. Consequently, by controlling thepressure in the space, the output braking moment may be adjusted. Beforethe retarder begins to produce an output braking moment, the spacebetween the stator and the rotor has to be filled with oil. Previously,the retarder has comprised a pump and an oil reservoir. The lower thespeed of the propeller shaft of the vehicle is, the longer time it taketo fill the space around the stator and the rotor. In order to speed upthis operation, an oil accumulator is often used in connection with theoil reservoir.

The working medium of a hydrodynamic retarder is any suitable oil. Asmentioned above, the kinetic energy of the oil is transformed to heatenergy during a braking process. In order to avoid overheating of theoil, it is important that the oil flow through the toroid-shaped spacebe high. With a high oil flow, one may obtain an effective cooling ofthe oil. In order to obtain a high flow of oil, the pressuredifferences, which are created when the rotor rotates in a certaindirection of rotation, are used. After the oil has left thetoroid-shaped space, the oil is guided to a cooling system/heatexchanger of the vehicle, such as a cooling water circuit in thevehicle. Thereafter, the oil may be returned to the toroid-shaped space.The cooled oil may be used for cooling the retarder. As a consequence ofthat, a great quantity of heat is produced by the retarder during abraking process. Furthermore, the working life of the oil is influencedby high temperatures, wherein the time which pass between the exchangeintervals decreases if the temperature of the oil is kept down.

FIG. 1 shows parts of a known retarder for a heavy vehicle, such as alorry. The known retarder comprises a double rotor 1 and two stators 2,3, which surrounds a shaft 4 to form two toroid-shaped spaces 5. Theinner diameter of the respective toroid-shaped space is used as an inlet6 and the outer diameter as an outlet 7. By having the inlet 6 inconnection to the inner diameter of the torus, a delivering channel 8has to be provided between the shaft 4 and the inlet 6. Hereby, thisretarder construction takes up a great deal of space. Furthermore, itought to be noted that when the rotor rotates, the pressure difference,which is created between the area where the inlets 6 are located and thearea where the outlets 7 are located is relatively small. Consequently,no higher flow of the working medium may be obtained by thisconstruction.

SUMMARY OF THE INVENTION

The object of the present invention is to eliminate the above-mentionedproblem. Especially, it is aimed at a hydrodynamic brake, which allows ahigh flow of the working medium through the toroid-shaped space, i.e. alarge quantity of fluid per time unit, which flows through thetoroid-shaped space of the brake. A large quantity of fluid per timeunit implies that the fluid also may work as cooling medium, wherein theheat energy generated during the braking process may be carried off bythe fluid. A further object of the present invention is to provide ahydrodynamic brake by which it is possible to obtain a large brakingmoment in spite of the small dimensions of the brake.

These objects are achieved by features of hydrodynamic brake.

Such a hydrodynamic brake has supply openings provided in the vicinityof that side of the vane of the stator where a relatively low pressureis created when the rotor rotates in a certain direction of rotation.This makes it possible to quickly obtain a braking moment. If thehydrodynamic brake is connected to the power train of the vehicle, thedriver of the vehicle will experience satisfaction when he brakes withthe retarder of the vehicle. Furthermore, that location of the supplyopenings offers the possibility of providing the brake directly adjacentto a rotating shaft without having to provide any supply channel betweenthe rotary shaft and the toroid-shaped space, which is the case in theknown brake initially described.

According to an embodiment of the invention, said supply opening islocated in a radially outer area of the stator. Advantageously, thesupply opening is located in this area since the pressure is lowest inthis area.

According to a further embodiment of the invention, the supply openinghas an orifice, which at least partly cuts through the bottom surface.The orifice may be provided such that it partly cuts through the vaneand partly cuts through the bottom surface. Alternatively, the wholeorifice may cut through the bottom surface. It ought to be noted that inthe outer area of the stator in connection to the second side of a vane,when the rotor rotates in said direction of rotation, hardly any fluidexists in said area at a low coefficient of fullness, i.e. when only afraction of the space between the stator and rotor is filled with fluid.Thus, the pressure is lowest in said area.

According to a further embodiment of the invention, said supply openingextends through the bottom surface.

According to a further embodiment of the invention, said supply openinghas a longitudinal axis, which is substantially perpendicular to theaxis of rotation. By the above mentioned location of the supply openingand since the supply opening has a longitudinal axis which issubstantially perpendicular to the axis of rotation, the supply of thefluid will occur in the flow direction of the fluid within thetoroid-shaped space. Hereby, the fluid stream in the space between thestator and the rotor will not be appreciably disturbed.

According to a further embodiment of the invention, said fluid isarranged to be supplied to said toroid-shaped space via a plurality ofsupply openings. Since the supply openings are provided in connection tothe outer diameter of the stator, a large supply area may be obtained inspite of the small dimensions of the retarder. With a large supply area,a quicker turn over of the oil may be obtained through the toroid-shapedspace.

According to a preferred embodiment of the invention, a supply openingis provided in substantially all pockets of the stator. Hereby, thebrake may be made very compact.

According to a further embodiment of the invention, said dischargeopening is provided in the vicinity of said first side of a vane of thestator. Consequently, one uses the pressure difference, which is createdon the respective sides of a vane of the stator during rotation of therotor, for the supply and discharge, respectively, of the fluid. Hereby,one may obtain a high flow of fluid through the toroid-shaped space.

According to a further embodiment of the invention, said dischargeopening is located in a radially outer area of the stator. Since both ofsaid supply opening and said discharge opening with advantage arelocated in said outer radial area of the stator, the stator and therotor may be located adjacent to the axis of rotation, which not ispossible with the brake which is accounted as known technique. Hereby,one may obtain a greater volume of the space between the stator and therotor according to the invention at the same time as the outerdimensions of the stator and the rotor are less than in the brake whichis accounted as known technique, i.e. the toroid-shaped space may beplace closer to the axis of rotation and the difference between theouter and inner diameter of the toroid-shaped space may be made greaterthan the corresponding difference of the brake according to the priorart technique, which has been accounted in the description, at the sametime as the brake according to the invention discloses a smaller outerdiameter than said known brake. Consequently, an advantage of the brakeaccording to the invention is that it requires less space than the brakeaccounted as prior art technique, i.e. one uses the space better.

According to a further embodiment of the invention, said dischargeopening has an orifice, which at least partly cuts through said bottomsurface. The orifice may be provided in such a way that it partly cutsthrough the vane and partly cuts through the bottom surface.Alternatively, the whole orifice may cut through the bottom surface. Itought to be noted that in the outer area of the stator in connection tothe first side of a vane where the vane protrudes from the bottomsurface when the rotor rotates in said direction of rotation, thepressure is highest since the fluid stream is thickest in this area.Hereby, the most effective discharge of the fluid is obtained when thedischarge opening ends in said area.

According to a further embodiment of the invention, said dischargeopening has a longitudinal axis, which is substantially parallel withthe axis of rotation. By the above-mentioned location of the dischargeopening and since the discharge opening has a longitudinal axis which issubstantially parallel with the axis of rotation, the discharge of thefluid will take place in the flow direction of the fluid in thetoroid-shaped space. Hereby, the fluid stream in the space between thestator and the rotor will not be appreciably disturbed.

According to a further embodiment of the invention, said fluid isarranged to be discharged via a plurality of discharge openings. Hereby,one may obtain a quick discharge of the fluid from the toroid-shapedspace. Furthermore, it ought to be noted that with the brake accordingto the invention, the quantity of fluid, which flows through thetoroid-shaped space, may amount to 500 l/min. As mentioned in theinitial description, the fluid is cooled after it has left thetoroid-shaped space and thereafter it is returned to the toroid-shapedspace. By the large cooled circulating fluid quantity, the fluid alsoworks as a cooling medium, which is arranged to remove the heat energyfrom the brake, generated during the braking process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now to be explained by a description of apreferred embodiment and with reference to the attached drawings.

FIG. 1 shows a cross-section through a portion of a hydrodynamic brakeof a vehicle according to known technique,

FIG. 2 shows a cross-section through a portion of a hydrodynamic brakeof a vehicle according to the invention,

FIG. 3 shows the stator according to FIG. 2,

FIG. 4 shows the location of the vanes, the supply openings and thedischarge openings in the stator according to FIG. 2,

FIG. 5 shows the section A—A of the stator according to FIG. 4 in whichthe location of a supply opening and a discharge opening is shown indetail.

FIG. 6 shows how the fluid flows in the stator at a low coefficient offullness.

FIG. 7 shows a corresponding section as shown in FIG. 5 and how thefluid flows at a low coefficient of fullness, and

FIG. 8 shows the stator and the rotor of the brake according to FIG. 2and the direction of rotation of the rotor.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a cross-section through a retarder in form of ahydrodynamic brake of a motor driven vehicle. The known retarder isaccounted in the initial description.

FIG. 2 shows a cross-section through a portion of a hydrodynamic brakein form of a retarder of a motor driven vehicle according to theinvention. The retarder comprises an annular stator 10 and an annularrotor 12 which each comprises an annular recess 14, 16. The statorcomprises a plurality of vanes 18 which are provided in the recess 14 ofthe stator, and the rotor 12 comprises a plurality of vanes 20 which areprovided in the recess 16 of the rotor 12, see also FIG. 8. In a mountedstate, the annular stator 10 and the annular rotor 12 surround a shaft22 in such a way that the recesses 14, 16 together form a toroid-shapedspace 24. The retarder is connected to the power train of the vehicle,for example at the propeller shaft 23 of the vehicle in connection tothe gearbox of the vehicle in order to allow braking of the drivingwheels of the vehicle. The retarder may be provided directly on thepropeller shaft 23 or via a gear unit 25 such as in FIG. 2. The stator10 is fixedly provided in the vehicle in a suitable way and the rotor isfixedly connected to the shaft 22. During propulsion of the vehicle, therotor 12 is arranged to rotate around an axis of rotation x in relationto the stator 10 in a direction of rotation a, cp. FIG. 8.

As is evident in FIG. 3 and FIG. 4, the stator 10 comprises a pluralityof the supply openings 26 and a plurality of the discharge openings 28.The supply openings 26 and the discharge openings 28 are located in anouter radial area 30 of the stator 10. Each of the respective supplyopenings 26 has a longitudinal axis y which is substantiallyperpendicular to the axis of rotation x and each of the respectivedischarge openings 28 has a longitudinal axis z which is substantiallyparallel to the axis of rotation x.

FIG. 5 shows in detail how a supply opening 26 and a discharge opening28 are located in relation to a vane 18 of the stator 10.

As is evident in FIG. 4 and FIG. 8, the vanes 18 of the stator 10 dividethe annular recess 14 of the stator in such a way that two adjacentvanes form a pocket 32 between each other. Likewise, the vanes 20 of therotor 12 divide the annular recess 16 of the rotor in such a way thattwo adjacent vanes 20 form a pocket 34 between each other. A bottomsurface 36 of the respective pocket 32 extends between two adjacentvanes 18 of the stator 10. Furthermore, the bottom surface 36 extendsbetween an outer radial edge 38 and an inner radial edge 40, see FIG. 3.Likewise, a bottom surface 42 of the respective pocket 34 extendsbetween two adjacent vanes 20 of the rotor 12, see FIG. 8. Furthermore,the bottom surface 42 extends between an outer radial edge (not shown)and an inner radial edge (not shown).

As be evident in FIG. 8, a pocket 32 of the stator 10 is open towards apocket 34 of the rotor 12. Furthermore, the vanes 18, 20 incline inrelation to the bottom surfaces 36, 42.

When the rotor 12 rotates around the axis of rotation x in the directiona, a relatively high pressure will be created on a first side 44 of therespective vane 18 of the stator 10 and a relatively low pressure on thesecond side 46 of the respective vane 18 of the stator 10, cp. FIG. 5.

During a braking process, a fluid/a working medium in form of ahydraulic liquid, for example any suitable oil, is arranged to besupplied to the toroid-shaped space 24, via the supply openings 26 ofthe stator 10, in order to brake the rotor 12 and consequently thedriving wheels of the vehicle. The fluid is discharged via the dischargeopenings 28 of the stator 10. During the braking process, the mediumwill be guided by the vanes 20 of the rotor 12 in a direction ofrotation a and radially outwards in the toroid-shaped space 24 along thebottom surface 42 of the pocket 34 and be thrown with a high velocityfrom the outer radial edge of a pocket 34 of the rotor 12 over to anouter radial edge 38 of a pocket 32 of the stator 10. The fluid hits thevanes 18 of the stator 10 and the motion of the fluid in the directionof rotation of the rotor 12 a is retarded and is guided by the vanes 18of the stator 10 radially inwards along the bottom surfaces 36 of thepockets 32 until it reaches the inner radial edge 40. Hereby, the fluidhits the rotating vanes 20 of the rotor 12 at an angle such that therotor 12 is braked.

In order to fill quickly or empty quickly the toroid-shaped space 24with fluid, one uses the pressure difference, which is created around arespective vane 18 of the stator 10. A quick turnover/circulation of theworking medium/the fluid through the toroid-shaped space 24 is obtained.In order to obtain as quick turnover of the working medium as possible,the supply openings 26 have an orifice 48, which cuts through the bottomsurface 36 in the vicinity of the second side 46 of a vane 18, see FIG.5. In this area, the pressure is lowest and at a low coefficient offullness, i.e. when only a fraction of the toroid-shaped space 24 isfilled with fluid, there is hardly any fluid in this area, see FIGS. 6and 7 which show how the fluid flows at a low coefficient of fullness.The discharge openings 28 have an orifice 50 which cuts through thebottom surface 36 in the vicinity of the first side 44 of a vane 18 ofthe stator 10, see FIG. 5. In this area, the pressure is highest and ata low coefficient of fullness the fluid exists only in this area, seeFIG. 7. With the hydrodynamic brake according to the invention, thepressure difference between the first side 44 of a vane 18 and a secondside 46 of the vane 18 maybe over 35 bar.

In order to disturb the fluid stream in the toroid-shaped space 24 aslittle as possible, the supply and discharge, respectively, of fluidoccur substantially in the flow direction. At the discharge opening 28,the flow direction is substantially parallel with the axis of rotationx. Consequently, the longitudinal axis z of the respective dischargeopening is substantially parallel with the axis of rotation x asmentioned above in connection to FIG. 3. At the supply openings 26, theflow direction is substantially perpendicular to the axis of rotation x.Consequently, the longitudinal axis y of the respective supply openingis substantially perpendicular to the axis of rotation x as mentioned inconnection to FIG. 3.

It ought to be noted that with the brake according to the invention, thequantity of fluid, which flows through the toroid-shaped space 24, maybe up to 500 l/min. As mentioned in the initial description, the fluidis cooled after it has left the toroid-shaped space 24 and thereafter itis returned to the toroid-shaped space 24. By the large cooledcirculating fluid quantity, the fluid also works as a cooling medium,which is arranged to remove the produced heat energy from the brakeduring the braking process.

The invention is not in any way restricted to the showed embodiment butmay be varied and modified within the scope of the following claims.

1. A hydrodynamic brake comprising: an annular stator with a statorrecess therein, an annular rotor opposite the stator with a rotor recesstherein, the stator recess and the rotor recess opening toward eachother to together define an annular toroid-shaped space; the stator andthe rotor are coaxial around an axis of rotation of the rotor; a firstplurality of vanes in the stator recess, a second plurality of vanes inthe rotor recess, with the vanes in each recess extending toward theother recess, each pair of adjacent vanes in each recess define arespective pocket between the vanes of the pair, the stator and rotoreach being shaped to define a bottom surface of each pocket between eachpair of adjacent vanes, each pocket has an outer radial edge and aninner radial edge; the vanes being oriented in their respective pocketsto define a first side of each vane in the rotation direction and anopposite second side of each vane opposite the rotation direction; thevanes being so located and oriented in their respective recesses thatupon rotation of the rotor around the axis in the rotation direction, ahigher pressure is developed on the first side of each vane of thestator and a lower pressure is developed on the second side of each vaneof the stator; at least one supply opening in the stator, arrangedcloser to the second side of each vane of the stator than to the firstside of the vane of each stator where there is a lower pressure, forsupplying fluid to the toroid-shaped space, wherein the fluid in thespace brakes the rotor during rotation; and at least one dischargeopening for the fluid from the space.
 2. The hydrodynamic brake of claim1, wherein the stator has a radially outer area, the fluid supplyopening is located in the radially outer area of the stator.
 3. Thehydrodynamic brake of claim 2, wherein the supply opening extendsthrough the bottom surface of the of the pocket between a pair ofadjacent vanes of the stator.
 4. The hydrodynamic brake of claim 1,wherein the supply opening includes an orifice which at least partlyextends through the bottom surface of the pocket between a pair ofadjacent vanes.
 5. The hydrodynamic brake of claim 1, wherein the supplyopening extends through the bottom surface of the of the pocket betweena pair of adjacent vanes of the stator.
 6. The hydrodynamic brake ofclaim 1, wherein the supply opening has a longitudinal axis which issubstantially perpendicular to the rotation axis of the rotor.
 7. Thehydrodynamic brake of claim 1, further comprising a plurality of thesupply openings to the toroid-shaped space, each supply opening locatedat the second side of a respective one of the vanes of the stator. 8.The hydrodynamic brake of claim 7, further comprising a plurality of thevanes of the stator, a plurality of the pockets between the pairs ofadjacent vanes in the stator and a respective supply opening in each ofthe pockets of the stator.
 9. The hydrodynamic brake of claim 1, whereinthe discharge opening is provided in the vicinity of the first side ofthe vanes in the stator.
 10. The hydrodynamic brake of claim 9, whereinthe stator has a radially outer area, and the discharge opening islocated in the radially outer area of the stator.
 11. The hydrodynamicbrake of claim 10, wherein the fluid supply opening is located in theradially outer area of the stator.
 12. The hydrodynamic brake of claim10, wherein the discharge opening extends through the bottom surface ofthe pocket of the stator between a pair of adjacent vanes.
 13. Thehydrodynamic brake of claim 9, wherein the discharge opening comprisesan orifice which at least partly cuts through the bottom surface of thepocket between the pair of adjacent vanes in the stator.
 14. Thehydrodynamic brake of claim 12, wherein the discharge opening has alongitudinal axis substantially parallel to the axis of rotation of thestator.
 15. The hydrodynamic brake of claim 14, wherein the supplyopening extends through the bottom surface of the of the pocket betweena pair of adjacent vanes of the stator and the supply opening has alongitudinal axis which is substantially perpendicular to the rotationaxis of the rotor.
 16. The hydrodynamic brake of claim 9, furthercomprising a plurality of the vanes of the stator each having the secondside thereof and a plurality of the discharge openings each in thepocket between a pair of adjacent vanes) with each discharge openingbeing near the first side of the respective vane of the pocket in whichthe discharge opening is located.